OBJECTIVE To assess the effect of dietary restriction and aging upon bone metabolism in rhesus monkeys. RESULTS Bone mass was lower in dietary restricted animals, however this reflects smaller body size and not pathological osteopenia. In addition, dietary restriction may protect against the development of spinal osteoarthritis. DISCUSSION The pathogenesis of age-related bone loss is unclear. As dietary restriction (DR) retards many aspects of aging, it may also alter skeletal changes. The purpose of this study was to examine the effects of moderate DR (30% reduction in caloric intake from individual baseline values) on bone. Bone mass (dual-energy X-ray absorptiometry), turnover (osteocalcin, ICTP, and NTx) and lumbar spine osteoarthritis (OA; radiographs) were examined longitudinally in male (15 Control [C], 15 Restricted [R]; after 96 months of DR) rhesus macaques 8-14 years of age at the onset of DR. Total body bone mass was lower in R compared to C males and females. In the females, R bone mass was also lower than C at the posterior-anterior spine and radius (except for distal radius bone mineral content). Serum turnover markers, and calcium and phosphorus concentration were not different between C and R groups. In addition, testosterone and FSH in the males were unchanged. There was less evidence of spi nal OA in R males. We believe the lower bone mass reflects the smaller body size, and not pathological osteopenia. In this model, DR does not cause deleterious endocrine effects and may afford protection against spinal OA. FUTURE DIRECTIONS We plan to continue using DXA, radiographs and markers of bone metabolism to better characterize the skeletal aging process in rhesus monkeys, making them better understood models for osteoporosis research. KEY WORDS osteoporosis, bone density, aging, bone metabolism, DXA FUNDING NIH PO1 AG11915